Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UMLS:C0030567 (Parkinson's disease)
 63,064 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Parkinson's disease (PD) is associated with degeneration of the pigmented dopaminergic neurons located in the ventral mesencephalon. Although the mechanisms by which these neurons degenerate in PD are poorly understood, indirect evidence suggests involvement of glutamatergic mechanisms in the pathogenesis of this disorder. Glutamate, the major excitatory transmitter in the mammalian central nervous system, is known to be neurotoxic when present in excess at the synapses. Two major mechanisms protect neurons from glutamate-induced toxicity: (a) removal of synaptic glutamate via a high affinity uptake carried out by cytoplasmic membrane proteins known as excitatory amino acid transporters (EAAT); and (b) metabolism and recycling of glutamate by synaptic astrocytes via glutamine synthetase, an ATP-requiring reaction. However, when extra-cellular glutamate levels are high (0.5-1.0 mM), glutamate metabolism may be shifted toward the ATP-generating oxidative deamination (glutamate dehydrogenase)-TCA cycle pathway. We have cloned and characterized two human glutamate dehydrogenases (GDH), one of which is nerve tissue specific. This isoenzyme requires ADP for its activity and it may become functional when cellular energy charge is low. We have also cloned three human glutamate transporters. One of these (EAAT3) is neuron specific. In situ hybridization studies using human brain revealed that the pigmented dopaminergic neurons, which degenerate in PD, express EAAT3 at high levels. Primary nerve tissue cultures derived from rat ventral mesencephalon were established and studied for their ability to metabolize glutamate. Results showed that mature cultures expressing high levels of GDH activity were capable of rapidly utilizing glutamate added to the medium at high concentrations (1-1.2 mM). This was associated with little release of aspartate and alanine into the medium. In contrast, immature cultures expressing low GDH activity utilized glutamate at lower rates while releasing substantial amounts of aspartate and alanine into the medium. These data suggest that immature mesencephalic cells metabolize a substantial fraction of the glutamate they take up from the medium via the transamination pathway, compared to mature mesencephalic cultures. Immunocytochemical studies on these cultures revealed that dopaminergic neurons (identified by their tyrosine hydroxylase content) showed intense staining for GDH. Furthermore, inhibition of GDH expression by antisense oligonucleotides was toxic to cultured mesencephalic neurons, with dopaminergic neurons being affected at the early stages of this inhibition. Hence, the dense expression by dopaminergic neurons of proteins involved in the transport and metabolism of glutamate may serve particular biological needs intrinsic to these cells. Further studies are required to test whether these properties render these neurons vulnerable to excitotoxic mechanisms or to abnormalities of glutamate metabolism.
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PMID:Glutamate transport and metabolism in dopaminergic neurons of substantia nigra: implications for the pathogenesis of Parkinson's disease. 1099 62

Six patients with idiopathic Parkinson's disease (IPD), six with clinically probable multiple system atrophy and six control subjects underwent quantitative proton magnetic resonance spectroscopy (MRS). The concentrations of the three major metabolites, N-acetylaspartate (NAA), creatine and choline, were quantified in the lentiform nucleus using tissue water content as an internal concentration reference. Glutamate was assessed as the (glutamate + glutamine)/creatine peak area ratio (Glx/Cre). In the control subjects the mean (+/- SD) concentrations of the three metabolites were 15.2 +/- 2.9 micromol/g wet weight for NAA, 12.0 +/- 1.4 for creatine and 2.4 +/- 0.3 for choline. The Glx/Cre ratio was 1.28 +/- 0.32. The only significant difference in any metabolite concentration was in the lentiform nucleus of patients with IPD compared with controls, with an increase in choline which lead to a significant reduction in the NAA/choline ratio. The relevance of this finding is uncertain. The results of the present pilot study, combined with the conflicting findings from previous work, suggest that further, much larger, studies are required to evaluate the diagnostic capability of proton MRS.
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PMID:Basal ganglia metabolite concentrations in idiopathic Parkinson's disease and multiple system atrophy measured by proton magnetic resonance spectroscopy. 1113 52

Glutamate is the predominant excitatory neurotransmitter of the basal ganglia, where it acts on ionotropic and metabotropic receptors. In the best studied of the basal ganglia disorders, Parkinson's disease, there is compelling evidence that the activities of glutamatergic pathways are altered. Of particular importance, the glutamatergic subthalamic nucleus becomes overactive. Pharmacologic blockade of subthalamic neurotransmission has antiparkinsonian symptomatic effects and may also help to protect the remaining dopamine neurons of the substantia nigra from excitotoxic neurodegeneration. Development of drugs to manipulate the glutamatergic system with appropriate pharmacologic and anatomic selectivity is likely to dramatically improve our ability to treat disorders of the basal ganglia.
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PMID:Glutamatergic influences on the basal ganglia. 1130 40

Glutamate is the major excitatory neurotransmitter of the central nervous system. Besides its importance in many physiological processes, increased glutamate release and subsequent excessive stimulation of the various glutamate receptors are thought to play critical roles in the pathophysiological mechanisms underlying many neurologic diseases. Experimental data suggest that blockade of glutamate receptors or inhibition of glutamate release has positive effects in many disease models. Glutamate antagonists are already in clinical use for the treatment of Parkinson's disease, epilepsy, spasticity, and neuropathic pain. Overall, glutamate antagonists have not been found clinically effective for neuroprotective treatment of cerebral ischemia or chronic neurodegenerative diseases, with one exception. Side effects of glutamate antagonists can be mainly attributed to central mechanisms and include psychosis, agitation, and disorientation. It is to be hoped that further development of new glutamate antagonists that block disease-relevant subtypes of glutamate receptors will lead to more effective drugs with fewer side effects.
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PMID:[Glutamate antagonists in neurology]. 1143 98

Glutamate is responsible for most of the excitatory synaptic activity and oxidative stress induction in the mammalian brain. This amino acid is increased in the substantia nigra in parkinsonism due to the lack of dopamine restraint to the subthalamic nucleus. Parkinson's disease also shows an increase of iron levels in the substantia nigra and a decrease of glutathione, the antioxidant responsible for the ascorbate radical recycling. Considered together, these facts could make the antioxidant ascorbate behave as a pro-oxidant in parkinsonism. Since both glutamate and ascorbate are present in the synaptosomes and neurons of substantia nigra, we tested 1) if glutamate is able to induce oxidative stress independently of its excitatory activity, and 2) if ascorbate may have synergistic effects with glutamate when these two molecules co-exist. Brains were homogenized in order to disrupt membranes and render membrane receptors and intracellular signaling pathways non-functional. In these homogenates glutamate induced lipid peroxidation, indicating that this amino acid also may cause oxidative stress not mediated by its binding to glutamate receptors or cystine transporters. Ascorbate also induced lipid peroxidation thus behaving as a pro-oxidant. Both substances together produced an additive effect but they did not synergize. Given that melatonin is a potent physiological antioxidant with protective effects in models of neurotoxicity, we tested the role of this secretory product on the pro-oxidant effect of both compounds given separately or in combination. We also checked the protective ability of several other antioxidants. Pharmacological doses of melatonin (millimolar), estrogens, pinoline and trolox (micromolar) prevented the oxidant effect of glutamate, ascorbate, and the combination of both substances. Potential therapeutic application of these results is discussed.
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PMID:Glutamate induces oxidative stress not mediated by glutamate receptors or cystine transporters: protective effect of melatonin and other antioxidants. 1170 66

Glutamate, an excitatory amino acid, is known to induce neurotoxicity in central nervous system under abnormal conditions such as ischemia, hypoglycemia, epilepsy, Huntington's chorea, Parkinson's disease and Alzheimer's disease. In our search for neuroprotective agents of microbial origin against excitatory neurotoxins, we have isolated two new bicyclohexapeptides, neuroprotectins A and B, together with a known compound complestatin, from the fermentation broth of Streptomyces sp. Q27107. Neuroprotectins protected primary cultured chick telencephalic neurons from glutamate- and kainate-induced excitotoxicities in a dose-dependant fashion.
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PMID:Neuroprotectins A and B, bicyclohexapeptides protecting chick telencephalic neuronal cells from excitotoxicity. I. Fermentation, isolation, physico-chemical properties and biological activity. 1185 54

The prominent pathological feature of the brain in Parkinson's disease is selective degeneration of dopaminergic neurons in the substantia nigra of the midbrain. Glutamate and nitric oxide (NO) are the major effectors of the radical stress that may induce selective loss of dopaminergic neurons. It has been postulated that neurotoxicity induced by glutamate and NO in dopaminergic neurons is regulated by certain endogenous factors. We have reported that estradiol protects dopaminergic neurons against NO-mediated glutamate neurotoxicity by reducing intracellular reactive oxygen species (ROS) levels. We further searched for a candidate for neuroprotective substances with unique structure. From the ether extract of fetal calf serum (FCS), we isolated a novel substance possessing protective activity against neurotoxicity induced by glutamate NO. The compound was a sulfur-containing diterpenoid and showed hydroxyl radical scavenging activity. We further analyzed the change of resistance to excitotoxicity in midbrain dopaminergic neurons in co-culture with the striatum by using a slice culture technique. The results suggested that the generation of NO is involved in NMDA cytotoxicity on dopaminergic neurons and that increased activity of SOD in co-culture renders dopaminergic neurons resistant to NMDA cytotoxicity by preventing peroxynitrite formation. Those findings suggest that regulation of intracellular ROS levels plays a critical role in protecting neurons against NO-mediated radical stress in neurodegenerative disorders.
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PMID:[Role of nitric oxide in survival and death of neurons]. 1186 52

DOPA seems to be a neuromodulator in striata and hippocampal CA1 and a neurotransmitter of the primary baroreceptor afferents terminating in the nucleus tractus solitarii (NTS) and baroreflex pathways in the caudal ventrolateral medulla and rostral ventrolateral medulla in the brainstem of rats. DOPA recognition sites differ from dopamine (DA) D(1) and D(2) and ionotropic glutamate receptors. Via DOPA sites, DOPA stereoselectively releases by itself neuronal glutamate from in vitro and in vivo striata. In the cultured neurons, DOPA and DA cause neuron death via autoxidation. In addition, DOPA causes autoxidation-irrelevant neuron death via glutamate release. Furthermore, DOPA released by four-vessel occlusion seems to be an upstream causal factor for glutamate release and resultant delayed neuron death by brain ischemia in striata and hippocampal CA1. Glutamate has been regarded as a neurotransmitter of baroreflex pathways. Herein, we propose a new pathway that DOPA is a neurotransmitter of the primary aortic depressor nerve and glutamate is that of secondary neurons in neuronal microcircuits of depressor sites in the NTS. DOPA seems to release unmeasurable, but functioning, endogenous glutamate from the secondary neurons via DOPA sites. A common following pathway may be ionotropic glutamate receptors-nNOS activation-NO production-baroreflex neurotransmission and delayed neuron death. However, we are concerned that DOPA therapy may accelerate neuronal degeneration process especially at progressive stages of Parkinson's disease.
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PMID:DOPA causes glutamate release and delayed neuron death by brain ischemia in rats. 1220 Jan 94

Chronically administered levodopa to Parkinson's disease (PD) patients ultimately produces alterations in motor response. Similarly, in 6-hydroxydopamine lesioned hemi-parkinsonian rats, chronic twice-daily administration of levodopa progressively shortens the duration of contralateral turning, an index of, the wearing-off fluctuations that occur in parkinsonian patients. The pathogenesis of these response alterations involves, in part, upregulation of corticostriatal glutamatergic synaptic transmission. Changes involving kinase and phosphatase signaling pathways within striatal dopaminoceptive medium-spiny neurons now appear to contribute to increased synaptic efficacy of glutamatergic receptors in these neurons. Glutamate-mediated striatal sensitization subsequently modifies basal ganglia output in ways that favor the appearance of parkinsonian motor complications. At the molecular level, transcriptional activation of striatal CREB and cdk5 may contribute to the persistent expression of these levodopa-induced response alterations. Conceivably, a safer and more effective therapy for PD can be provided by drugs that target signaling proteins within striatal spiny neurons or those that interact extracellularly with non-dopaminergic receptors such as AMPA and NMDA, adenosine, adrenergic, opioid, and serotonergic.
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PMID:Glutamate-mediated striatal dysregulation and the pathogenesis of motor response complications in Parkinson's disease. 1237 27

Glutamate is the most widely distributed excitatory transmitter in the central nervous system (CNS). It is acting via large - and still growing - families of receptors: NMDA-, AMPA-, kainate-, and metabotropic receptors. Glutamate has been implicated in a large number of CNS disorders, and it is hoped that novel glutamate receptor ligands offer new therapeutic possibilities in disease states such as chronic pain, stroke, epilepsy, depression, drug addiction and dependence or Parkinson's disease. While an extensive preclinical literature exists showing potential beneficial effects of NMDA-, AMPA-, kainate- and metabotropic receptor ligands, only NMDA receptor antagonists have been characterized clinically to any appreciable degree. In these trials it has been shown that while several compounds are therapeutically active, they also produce serious side effects at therapeutic doses. Current interest largely centers on the development of receptor subtype-selective compounds, namely compounds selective for receptors containing the NR2B subunit. Preclinical findings and the first clinical results are encouraging, and it may be that such subunit-selective compounds may have a sufficiently wide therapeutic window to be safe for human use.
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PMID:Glutamatergic mechanisms in different disease states: overview and therapeutical implications -- an introduction. 1237 29


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